High data rate simulcast communication system

ABSTRACT

A system for transmitting long text messages includes a plurality of transmission cells defining different geographical areas, each having a transmitter for simulcast address transmission at a first data bit rate and for transmitting the address and a message at a second data bit rate higher than the first data bit rate. A paging transceiver generates and transmits an acknowledgment signal in response to receiving a transmitted address at the first data bit rate. Receivers located within each of the transmission cells receive the transmitted acknowledgment signal. An apparatus responsive to the received acknowledgment signal identifies the transmission cell in which the paging transceiver is located effecting the selection of the transmitter in the transmission cell in which the paging transceiver is located to transmit the address and message at the second data bit rate higher than the first data bit rate.

This is a division, of application Ser. No. 07/257,904, filed Oct. 13,1988 now U.S. Pat. No. 4,918,437.

FIELD OF THE INVENTION

This invention relates to the field of data communication systems, andmore particularly to a data communication system providing simulcastradio frequency data transmission capability for long data messagestransmitted at high data rates.

BACKGROUND OF THE INVENTION

Numerous data communication systems are available providing data messagedelivery. One such system having great popularity, the radio pagingsystem, can deliver numeric and alphanumeric messages originated by acaller, using a telephone or an alphanumeric messaging terminal. Themessages are then transmitted to a numeric or alphanumeric displaypager. Radio paging systems deliver the messages using a variety ofsignaling formats, such as the Golay Sequential Code (GSC) and POCSAGsignaling formats to small portable receivers referred to as pagers. ThePOCSAG signaling format is shown in FIG. IA. As shown, a synchronizationcode (SC) is first transmitted, which is used by all paging receivers,or pagers, within the system for maintaining synchronization with thetransmitted information. The synchronization code (SC) is followed byeight frames, F1-F8. Each frame provides for the transmission of addressblocks (A) and data blocks (M). Pagers are assigned to a specific one ofthe eight frames, providing the pager a battery saving function. Thepagers are generally configured as tone-only pagers (T) responding onlywith an audible alert when paged, numeric pagers (N) responding with anaudible alert and a displayed numeric message, such as a telephonenumber when pages, or alphanumeric pagers (Alpha) responding with anaudible alert and a displayed alphanumeric message when paged. Thepaging system transmits only the address identifying the pager beingpaged for tone-only pagers, and an address identifying the pager towhich a message is intended followed by the message for numeric andalphanumeric pagers. As shown in FIG. 1A, two tone-only address blockscan be transmitted in a single frame, while a simple seven digit phonenumber, which is encoded using a four bit binary data format, requirestransmitting an address block followed by two data blocks, continuingpart of the message into the next POCSAG frame. Alphanumeric messages,which are encoded using a seven bit BCH data format, can extend intomany frames and required substantially more air time to transmit thaneither the tone-only or numeric pages. Consequently, the transmission ofnumeric and alphanumeric messages on a paging system reduced the numberof pagers that can be loaded into the system, and this problem iscompounded when long alphanumeric messages are transmitted. One solutionwhich has been proposed for this problem is to increase the datatransmission rate to 1200 bits per second from the current standard 512bits per second. However, even this solution has proven inadequate fortransmitting long data messages.

In order to obtain the message throughput required to handle longalphanumeric messages, substantially higher data rates, such as at 2400or 4800 bits per second, or even higher are required. However, mostpaging systems in use today employ simulcast transmission of informationto provide wide area coverage. Such paging systems employ a number oftransmitters geographically separated, which are located in a cellular,or pseudo-cellular, fashion to provide the required coverage, and alltransmitters transmit the same information simultaneously in all cellsor zones. While conventional frequency modulated (FM) simulcasttransmission systems can provide adequate message transmission at datarates below 2400 bits per second, they become difficult to set up andhave not reliably been used to transmit messages at higher data rates.Problems, such as with providing proper phase equalization andsynchronization of the transmission of the transmitters within thesystem become substantially more difficult at higher data rates.

Another problem that exists in the transmission of long messages, isinsuring the message being transmitted, has been received by the pagerfor which it is intended, otherwise valuable air-time is wasted. Failureto receive the message can occur when the pager is out of range of thetransmitters, has not been turned on by the user, has a dead battery, orhas a battery that has died during the operating day. In providing apaging system capable of transmitting long messages, it is extremelyimportant to know the messages being transmitted are likely to bereceived, otherwise valuable air-time is lost.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide acommunication system providing increased message throughput.

It is a further object of the present invention to provide acommunication system providing increased message throughput utilizingsimulcast transmitter operation.

It is a further object of the present invention to provide acommunication system providing reliable message throughput at high datatransmission rates.

Generally, a system for transmitting long text messages includes aplurality of transmission cells each having a transmitter for simulcastaddress transmission at a first data bit rate and for transmitting theaddress and a message at a second data bit rate higher than the firstdata bit rate. A paging transceiver generates and transmits anacknowledgement signal having predetermined characteristics in responseto receiving the transmitted address at the first data bit rate.Receivers located within each of the transmission cells receive thetransmitted acknowledgement signal. A selecting means responsive to thereceived acknowledgement signals selects the transmission cell in whichthe paging transceiver is located effecting the transmission of theaddress and message at the second data bit rate higher than the firstdata bit rate in the selected transmission cell in which the pagingtransceiver is located.

Another embodiment of a system for transmitting long text messagesincludes a plurality of transmission cells each having a transmitter forsimulcast address transmission at a first data bit rate and fortransmitting the address and a message at a second data bit rate higherthan the first data bit rate. A paging transceiver generates andtransmits an acknowledgement signal having predetermined characteristicsin response to receiving the transmitted address at the first data bitrate. Receivers located within each of the transmission cells receivethe transmitted acknowledgement signal. A selecting means responsive tothe received acknowledgement signals selects the transmission cell inwhich the paging transceiver is located, and further selects one or moretransmission cells adjacent the transmission cell in which the pagingtransceiver is located for effecting the simulcast transmission of theaddress and message at the second data bit rate higher than the firstdata bit rate in the selected transmission cell in which the pagingtransceiver is located and in the selected adjacent transmission cells.

These and other objects and advantages of the present invention willbecome more apparent to those skilled in the art by referring to thefollowing detailed description and accompanying diagrams.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention which are believed to be novel are setforth with particularity in the appended claims. The invention itself,together with its further objects and advantages thereof, may be bestunderstood by reference to the following description when taken inconjunction with the accompanying drawings, in the several figures ofwhich like reference numerals identify identical elements, in which andwherein:

FIG. 1 is a timing diagram showing an example of data transmissionutilizing the POCSAG signaling format.

FIG. 2A is a line drawing depicting the simulcast transmission mode inthe preferred embodiment of the present invention.

FIG. 2B is a line drawing depicting the non-simulcast transmission modefor high data rate messages in the preferred embodiment of the presentinvention.

FIG. 2C is a line drawing depicting the pseudo-simulcast transmissionmode for high data rate messages in the preferred embodiment of thepresent invention.

FIG. 3 is a timing diagram showing the signaling format of the preferredembodiment of the present invention.

FIG. 4 is a timing diagram showing the application of the signalingformat of FIG. 3 in a simulcast transmission system.

FIG. 5 is a line drawing showing the flow of data and controlinformation for the simulcast transmission system described in FIG. 4.

FIGS. 6A and 6B are electrical block diagrams of the central stationtransmission facility and the remote site transmission facilities of thepreferred embodiment of the present invention.

FIG. 7 is an electrical block diagram showing a paging transceiver inthe preferred embodiment of the present invention.

FIGS. 8A-C are flow charts showing the operation of the central stationtransmission facility.

FIGS. 9A-C are flow charts showing the operation of the remote sitetransmission facilities.

FIGS. 10A-C are flow charts showing the operation of the pagingtransceivers of the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

With respect to the figures, FIGS. 2 through 10 illustrate in generalseveral preferred embodiments of the present invention. Referring toFIG. 2A, a typical simulcast communication system 10 is shown whichincludes a substantially centrally located central station 12(identified by the letter C) surrounded by a plurality of remotestations 14 (identified by the numbers 1-8). System 10, as shown in FIG.2A, is arranged in a substantially cellular pattern, comprising aplurality of transmission cells 16 defining different geographical areaswherein the central station 12 and remote stations 14 are located,thereby providing wide area coverage for a plurality of communicationtransceivers, such as paging transceivers 18, operating within thesystem. While system 10 shows a regular arrangement of transmissioncells 16, it will be appreciated by one of ordinary skill in the art,that the arrangement of transmission cells 16 need not be regularlydistributed to provide a wide area simulcast transmission system for aparticular geographical area. It will also be appreciated that thenumber of remote stations which is shown is for example only, anddepending upon the area of coverage, the system may have more or lessremote stations than shown. It will also be appreciated, that thelocation of central station 12 relative to that of remote stations 14,need not necessarily be centrally located, as shown, so long as centralstation 12 be able to communicate with remote stations 14 in the mannerto be described shortly.

Messages are entered into system 10 via central station 12 and formattedinto a predetermined signaling format having address and messagesegments, to be described in detail shortly. The formatted messages arestored for a predetermined time interval, also to be described in detailshortly, after which they are transmitted as a burst signal, or packetof information, at a very high data rate, such as 19.2 or 38.4 kilobitsper second for the preferred embodiment of the present invention, fromcentral station 12 to remote stations 14. The address segments of theburst signal are then simulcast from remote station 14 and centralstation 12 on a common radio (R.F.) frequency in a manner well known toone of ordinary skill in the art. The address segments are transmittedat a first data bit rate, such as 512 or 1200 bits per second, therebyproviding reliable simulcast transmission to the plurality of pagingtransceivers 18 operating within system 10. It will be appreciated thatother bit rates may also be employed, particularly when other signalingformats are employed, and that the preferred embodiment of the presentinvention is not limited to the data transmission rates indicated byexample. Each paging transceiver 18 is assigned a unique address towhich it is responsive. Upon receiving and detecting an addresscorresponding to the assigned address for each paging transceiver 18,each addressed paging transceiver 18 generates an acknowledgement signalin a manner to be described in detail shortly. The acknowledgmentsignals, which have predetermined characteristics, such as apredetermined transmission frequency, signal strength and signal phasecharacteristics, are generated by paging transceivers 18. Thetransmitted acknowledgement signals are received at one or more remotestations 14 or central station 12. The received acknowledgment signalsallow system 10 to identify the transmission cells 16 in which eachresponding paging transceiver 18 is located. Once the location of pagingtransceivers 18 have been determined, the messages, which are stored atcentral station 12, corresponding to each paging transceiver 18 aretagged identifying one or more remote stations 14 to be used in thesubsequent transmission of the message.

The tagged messages are transmitted at the burst signal data ratedescribed previously to the remote stations on the next central stationtransmission cycle. While all remote stations 14 receive the taggedmessages, only those remote stations to which the messages are tagged,process the messages as will be described shortly. Messages received atthe appropriate remote stations 14 are re-transmitted in one of twoembodiments of the present invention by the remote stations at a seconddata bit rate higher than the first data bit rate, such as 2400 or 4800bits per second. It will be appreciated that the bit rates indicated areby way of example only, and that other bit rates may be satisfactorilyemployed. In the first embodiment of the present invention shown in FIG.2B, the messages are transmitted only from the remote stations 14transmitter within the transmission cell 16 where the acknowledgingpaging transceiver 18 was located. This method allows interference freetransmission of lengthy messages on a common R.F. frequency withoutinterference to the other paging transceivers 18 also receiving lengthymessages in other transmission cells. Interference-free transmission isassured by providing simultaneous message transmission in non-adjacenttransmission cells. Where simultaneous message transmission isanticipated within adjacent transmission cells, the transmission fromone cell to the next would be delayed so as to avoid interference of thetwo messages.

In the second embodiment of the present invention shown in FIG. 2C,messages are transmitted in a manner similar to the description of FIG.2B, except that selected remote station transmitters in transmissioncells 16 adjacent to the transmission cell in which portable transceiver18 is located are used to provide a localized pseudo-simulcasttransmission of the messages. Pseudo-simulcast transmission requires themeasurement of the propagation delay of the acknowledgment signal to thecentral station and each of the remote stations. Once the propagationdelays have been determined, the differential propagation delays betweenthe central station and the remote stations can be determined. Thisinformation together with the location of the paging transceiverdetermined using the received signal strength permits the selection ofone or more additional transmitters in adjacent transmission cells to beused for transmission thereby allowing high data bit rate transmissionswithout experiencing large differential propagation delays which wouldotherwise corrupt the transmission. Information on differentialpropagation delays can be included with the address and messageinformation during the transmission of the burst signal allowing phasingcorrections to be made for the transmissions of adjacent remote stationtransmitters. Such pseudo-simulcast transmission is advantageous inproviding more reliable message delivery, especially in those geographicareas common between adjacent transmission cells 16, and in otherlocations such as buildings, where transmission losses from a particulartransmitter may be extremely high so as to degrade message delivery.Compared to the single transmitter transmission of FIG. 2B, a 3 dBimprovement in signal strength is obtained with two stations operating,a 5 dB improvement is obtained with three stations operating, and a 6 dBimprovement is obtained with four stations operating. Beyond fourstations, the complexity of phase correcting the transmissions ofmultiple stations for the high bit rate transmissions becomes extremelycomplex. Pseudo-simulcast transmission of messages also minimizes theproblem of transmitting different messages in adjacent transmissioncells, as previously described in the non-simulcast mode of operation.

FIG. 3 shows a timing diagram of the signaling format 100 of thepreferred embodiment of the present invention. Signaling format 100comprises a transmission time interval for the burst signal 102, duringwhich the burst signal is transmitted at the very high data ratepreviously described, from the central station to the remote stations. Adetailed description of burst signal 102 will be described in FIG. 4.

Returning to FIG. 3, a synchronization codeword (SC) 104 follows burstsignal 102. Synchronization codeword 104 is used by the pagingtransceivers to maintain synchronization with the system in a mannerwell known to one of ordinary skill in the art. Such synchronizationallows for decoding of addresses and messages to follow, as well as forbattery saving purposes.

Address segment 106, shown in FIG. 3, follows synchronization codeword104. The POCSAG signaling format is shown for example in address segment106 of the preferred embodiment of the present invention and compriseseight frames 108. Each frame includes two address codewords 110,providing for the transmission of two addresses per frame. Each addresscodeword 110 is a thirty-two bit binary codeword comprising a 31,21 BCHcodeword and a single block error check bit, as is well known in thePOCSAG signaling format. The addresses are transmitted at the first databit rate previously described. It will be appreciated by one of ordinaryskill in the art that other signaling formats, such as the GolaySequential Code, or GSC signaling format, could also be used in thedelivery of addresses during address segment 106.

Silent carrier (CW) 112, shown in FIG. 3, follows address segment 106.During this time interval, unmodulated or silent carrier is simulcasttransmitted by the central and remote stations in the system. Silentcarrier (CW) 112 is used by the paging transceivers to adjusttransmitter frequency and power output prior to the transmission of anacknowledgement signal acknowledging the reception of the address,thereby guaranteeing known acknowledgement response characteristics. Thetransmitter frequency adjustment process is described in detail incopending U.S. patent application Ser. No. 07/141,655, filed Jan. 7,1988, entitled "Acknowledge Back Pager with Apparatus for ControllingTransmit Frequency", and U.S. patent application Ser. No. 07/141,653,filed Jan. 7, 1988, entitled "Acknowledge Back Pager with FrequencyControl Apparatus". The power output level adjustment is described incopending U.S. patent application No. 07/141,370, filed Jan. 7, 1988,entitled "Acknowledge Back Pager with Adaptive Variable TransmitterOutput Power". The three applications are assigned to the assignee ofthe present invention, and are hereby incorporated for reference herein.

Message segment 114, shown in FIG. 3, follows silent carrier (CW) 112.Message segment 114 includes a plurality of message blocks 116corresponding to addresses transmitted during the previous transmissioncycle. Each message block 116 includes transmitter control informationidentifying one or more remote stations which will be used to transmiteach message, the address associated with the message, and an end ofmessage indicator, which is shown in greater detail in FIG. 4. Unlikeaddress segment 106, it will be appreciated message segment 114 is not afixed number of data blocks in length, but rather varies depending uponthe length of the message to be transmitted. Message segment 114 istransmitted at the second data bit rate of 2400 or 4800 bits per second,as previously described. The second data bit rate provides for thetransmission of two to eight times the message length in a time intervalequal to the first data bit rate of 512 or 1200 bits per second, therebygreatly increasing message throughput.

Acknowledgement signals (PACKS) 118, shown in FIG. 3, are transmittedsimultaneously by all paging transceivers having received and detectedan address during address segment 106. PACKS 118 can be encoded byseveral methods, one of which is described in copending U.S. patentapplication Ser. No. 07/141,654 filed Jan. 7, 1988, entitled "FrequencyDivision Multiplexed Acknowledge Back Paging System", which is assignedto the assignee of the present invention, and is hereby incorporated forreference herein. Patent application Ser. No. 07/141,654 describes afrequency division multiplex method allowing a group of pagingtransceivers to simultaneously acknowledge during a common timeinterval. In the preferred embodiment of the present invention, sixteenpaging transceivers are shown potentially responding, although it willbe appreciated that more or less paging transceivers may acknowledge inthe time interval provided. An alternate embodiment for encoding theacknowledgement signals for simultaneous transmission to the remotestations is described in copending U.S. patent application Ser. No.7/141,656, filed Jan. 7, 1988, entitled "Code Division MultiplexedAcknowledge Back Paging System", which utilizes orthogonal codes toprovide code division multiplexing of the encoded acknowledgementsignals onto a common carrier frequency, which is hereby incorporated byreference herein.

PACKS 118, received at the central and remote stations, are processed toidentify the responding paging transceivers, and to determined thereceived signal strength at each remote station. Processing of thereceived PACKS include decoding the PACKS, error correcting theresultant information, and re-encoding the resultant information forSACK transmission. This results in enhanced reliability in the locationof responding paging transceivers. Time of acknowledgement reception mayalso be obtained at this time, as will be described in detail later. Thereceived signal strength and time of reception information is encodedinto a suitable format for transmission from the remote stations to thecentral station during the system acknowledgement time interval (SACKS)120. SACKS 120 are transmitted from the remote stations to the centralstation also at a high data bit rate, such as 9600 bits per second. Oncethe received signal strength and time of reception information isreceived from all remote stations in the system, the information isprocessed at the central station to identify the transmission cellshaving paging transceivers acknowledging the addresses transmittedduring address segment 106. The messages corresponding to the addressestransmitted during address segment 106 are tagged to indicate in whichtransmission cell each paging transceiver is located. This taggedmessage information is then temporarily stored and transmitted to thepaging transceivers during the next transmission cycle.

The operation of simulcast transmission system 10 utilizing transmissioncycle 100 will be better appreciated by considering FIG. 4 which shows atiming diagram of the operation of a typical simulcast systemincorporating the preferred embodiment of the present invention. Asmessages are inputted into the system, they are stored in a memory, tobe described shortly, which is depicted by active page file 200. Activepage file 200 includes a synchronization codeword 202 followed by acurrent frame address segment 204 and a current frame-1 data segment.The current frame address segment 204 corresponds to address segment 106previously described, while the current frame-1 data segment 206corresponds to message segment 114 previously described. As also shownin FIG. 4, current frame address segment 204, may also be used incertain instances for message transmission, such as for very shortmessage paging where the message is no more than one address block inlength. When messages are transmitted in current frame address segment204, they are positioned at the end of the address segment, as shown, asacknowledgement responses are determined by the order of addresstransmission as described in copending patent application Ser. No.07/141,654.

Current frame-1 data segment 206, shown in FIG. 4, contains the messageinformation corresponding to the addresses transmitted in the previoustransmission cycle. The current frame-1 data segment 206 includestransmitter control codewords 208 followed by paging transceiveraddresses 210, messages 212 and end-of-message (EOM) delimiters 213.Transmitter control words 208 identify the transmission cells in whichresponding paging transceivers were located during the previoustransmission cycle. The active page file 200 is transmitted from thecentral station to the remote stations during the burst signal 102transmission.

Following the receipt of the active page file 200 by the remotestations, the synchronization codeword 202 and current frame addresssegment 204 are simulcast by the central and remote stations. Followingthe transmission of the current frame address segment 204, the centralstation and remote stations transmit an interval of silent carrier 215,during which time the paging transceivers receiving the addressestransmitted in the address segment adjust transmit frequency and poweroutput. The current frame-1 data segment 206 is then transmitted in anon-simulcast or pseudo simulcast manner from those stations, central orremote, designated as having paging transceivers located in theirtransmission cells, as previously described.

The transmission cycle is further understood by considering the specificexample of the operation of the central and remote stations as shown inFIG. 4. Remote station #1 was determined during the previoustransmission cycle to have two paging transceivers located within itstransmission cell, paging transceivers corresponding to addresses Alland A12. Furthermore, remote station #8 was determined to have a singlepaging transceiver located within its transmission cell, pagingtransceiver AlN. As previously described, as burst signal 214 wasreceived at each remote station, the information corresponding to thecurrent frame-1 data segment 206, is processed. Consequently, onlyremote stations 1 and 8, which were tagged as having responsive pagingtransceivers, accepted messages from the current frame-1 data segment206. In this case, remote stations 1 and 8 independently andsimultaneously transmitted the messages processed during the messagesegment 206 reception. As shown, such a system benefits by providingfrequency reuse of a single channel which results in increased messagethroughput by transmitting different messages in those transmissioncells where the individual paging transceivers are located. The centraland remaining remote stations, as shown, remained unkeyed during thetransmission of the current frame-1 data segment 206.

As previously described, those paging transceivers receiving addressesduring address segment 204, acknowledged receipt of the address duringthe PACK 216. The PACKS received at the various remote stations areprocessed, and then retransmitted to the central station during theSACKS 218 time interval. As shown in FIG. 4, the SACKS are transmittedback in a sequential manner starting in numeric sequence with thecorresponding remote stations. This information received at the centralstation is used to tag the current frame data which is then transmittedin the next transmission cycle. Should any paging transceiver benon-responsive, those messages are stored, and after a period of time,such as five minutes, and the non-responsive paging transceiver addressis again re-transmitted in an attempt to locate the paging transceiver.Air time is saved by not transmitting messages to a non-responsivepaging transceiver. If the paging transceiver again does not respond,the message may again be stored for transmission at a later time.

FIG. 5 shows a line drawing of the transmission sequences performed inthe preferred embodiment of the present invention, and is used to recapthe previous operations described. The central station transmits burstsignal 300 containing address and message segments at a very high datarate to the remote stations. This information is received at the remotestations and processed for re-transmission. The synchronization codewordand the address segments are simulcast transmitted by central and remotestations 302 at a data rate insuring reliable simulcast transmissionthroughout the system. The central and remote stations then simulcasttransmit silent, or unmodulated carrier 304 for a duration sufficientfor the responsive paging transceivers to adjust their transmittingfrequency and output power. Next, the remote stations which were taggedas having paging transceivers located within each station's transmissioncell on the previous transmission cycle, individually transmit themessages in a non-simulcast or pseudo simulcast manner, at a high datarate, thereby efficiently delivering long data messages 306. Theresponsive paging transceivers during the address segment transmissionthen acknowledge receipt of the address by transmitting anacknowledgement signal to the remote stations 308, thereby allowing thesystem to locate the transmission cell in which the responsive pagingtransceivers are located, for use during the next transmission cycle.The remote stations next transmit the received signal strength and timeof signal reception information derived from the receivedacknowledgement signals to the central station 310 sequentially at ahigh data bit rate. The information is processed and is used to tag themessages to be re-transmitted during the next transmission cycle. Thecentral station then assembles a new active page file and transmits thisinformation to the remote stations 312, thereupon initiating a newtransmission cycle.

FIGS. 6A and 6B show electrical block diagrams of central station 12 andremote stations 14, respectively, for the preferred embodiment of thepresent invention. As can be seen in the drawings, the central station12 and remote site stations 14 share substantially the sameconfigurations. The central station includes telephone interconnect 400and paging terminal 402 not found in the remote site stations, whereasremote stations 14 include synchronizing means 426 not found in thecentral station, the functions of which will be described in detailshortly.

Referring to FIG. 6A, central station 12 comprises telephoneinterconnection means, or telephone interconnect 400, which allowsmessages to be entered into the system through the telephone networkusing a telephone or alphanumeric entry device. Telephone interconnect400 couples to paging terminal 402 which processes the informationreceived through telephone interconnect 400. The information processedby paging terminal 402 may be DTMF or dial pulse encoded signals fortelephone encoded information, or binary data suitably encoded fortransmission over the phone line, such as with a modem, for alphanumericentry device messages. Paging terminal 402 generates the appropriatepaging transceiver address and stores the address and message in theactive page file portion of memory 404 until the next transmissioncycle. Paging terminals suitable for use in the preferred embodiment ofthe present invention are well known to one of ordinary skill in theart.

Paging terminal 402 couples to controller 406 which controls theoperation of link transmitter 408, paging transmitter 410, link receiver412 and the acknowledgement or PACKS receiver 414. Paging transmitter410 is a conventional direct FM (frequency modulated) transmitter, whichis well known to one of ordinary skill in the art. The PACKS receiver,is an FM receiver having a very narrow IF bandwidth, such as a 120 to150 Hz bandwidth which provides a 20 dB improvement in receivesensitivity over a conventional FM receiver having a typical IFbandwidth of approximately 12 to 15 KHz. The increased receivesensitivity allows PACK transmissions from the paging transceivers atlow power levels, such as 1 to 2 watts, as compared to the pagingtransmitter power of 100 watts. Minimizing the power required totransmit the acknowledgement signals results in increased battery lifefor the paging transceivers. The central station link transmitter, andremote station link receivers which operate at very high bit rates canutilize linear modulation techniques, such as MSK (minimum shift keying)modulation, which is well known to one of ordinary skill in the art.Other modulation techniques, such as employing high spectral efficiencydigital modulation techniques are also desirable. One example of such amodulation technique is described in Steel et al U.S. Pat. No.4,737,969, issued Apr. 12, 1988, entitled "Spectrally Efficient DigitalModulation Method and Apparatus" which is assigned to the assignee ofthe present invention, and which is incorporated by reference herein.

Controller 406 may be implemented using a microprocessor, such as aMotorola MC6809 or a Zilog Z80, or a microcomputer with suitableinterface circuitry for controlling the selection and operation of thecentral station transmitters and receivers. Controller 406, couples tolink transmitter 408, keying the link transmitter to transmit burstsignal to the remote stations. Controller 406 also couples to pagingtransmitter 410, keying the paging transmitter to transmit the activepage file within the transmission cell of central station 12. Controller406 also couples to link receiver 412, enabling the link receiver forthe reception of the SACKS, or system acknowledgement signals generatedat the remote stations. Controller 406 also couples to PACKS receiver414 enabling the receiver for the reception of the paging transceivergenerated acknowledgement signals.

Timing means 416 provides a high accuracy clock which couples tocontroller 406 to maintain system timing for simulcast operation throughsynchronization of all remote stations. A high stability referenceoscillator can be used for timing means 416. The reference clockfrequency generated by timing means 416 is at least ten times higherthan the highest address and message data bit rate used duringpseudo-simulcast message transmissions. This provides the accuracyrequired for the determination of differential propagation delays whichis required for the high speed transmission of address and messages inthe pseudo-simulcast transmission mode. In an alternate embodiment ofthe present invention, the received acknowledgement signals are suppliedto phase comparator 420, which compares the received acknowledgementsignals with a reference clock output 417 of timing means 416 todetermine the time of reception at each station receiving the PACKsignals. The output of phase comparator 420 couples to encoder 422 forencoding the generated time of reception signals into a format suitablefor processing by controller 406.

The output of PACKS receiver 414 couples to a received signal strengthindicator (RSSI) 418 which is used in determining the location of theacknowledging paging transceivers. Received signal strength indicatorssuitable for determining received signal strength are well known to oneof ordinary skill in the art. During the reception of the PACKS, thereceived signals are monitored by signal strength indicator 418. Signalstrength indicator 418 generates a signal strength indication signalwhich also couples to encoder 422, such as an A/D converter which iswell known in the art, for encoding into a format suitable forprocessing by controller 406. Controller 406 evaluates the signalstrength information from each station to determine the transmissioncell in which each responding paging transceiver is located.Differential propagation delays are computed from the time of receptionsignals, or measured propagation delay information measured at eachremote station. This information is used to adjust the timing or phasefor the pseudo-simulcast transmission of current frame-1 data segment atthe high data bit rates.

As described above, it will be appreciated, the signal strengthindicator 418, link transmitters 428 at the remote stations, apredetermined link receiver, such as link receiver 412 at the centralstation, and controller 406 at the central station function as anidentifying means 407 for identifying the transmission cell in which thepaging transceiver is located. These elements, together with the timingmeans 416 and phase comparator 420, function as the identifying meansfor identifying the transmission cell in which the paging transceiver islocated, and at least one additional transmission cell adjacent to thetransmission cell in which the paging transceiver is located. Apredetermined link transmitter, such as link transmitter 408 at thecentral station, link receivers 412 at the remote stations, and sitecontroller 430 at the remote stations function as the selecting means409, used to accept messages tagged to particular remote stations andfor selecting the remote station transmitter for transmitting theaccepted messages. The criteria for transmission cell selection is veryflexible. In periods of low long message traffic, the pseudo-simulcasttransmission format is preferred. The pseudo-simulcast transmissionformat combines messages directed to specific transmission cells to thegroup of transmission cells selected for pseudo-simulcast transmission.This increases the relative traffic for long messages in each of thetransmission cells, thereby allowing shorter time intervals to thetransmission of the messages since messages can be stored in queues atthe remote station for more than one transmission cycle. The number oftransmission cycles during which messages are stored before transmissionis a function of several factors, such as stability of the pagingtransceiver acknowledgment transmitter oscillator and likelihood of thepaging transceiver to move from one transmission cell to another. Thegreater the paging transceiver transmitter oscillator stability andlower likelihood of movement to another cell after the pagingtransceiver has adjusted the transmit frequency and power output duringthe initial silent carrier transmission, the greater the number oftransmission cycles can be used to store messages at the remote stationbefore transmission.

As previously described, locating of the paging transceiver in aparticular cell is based on received signal strength. The transmissioncell receiving the strongest received signal from a particular pagingtransceiver is selected as the transmission cell in which the pagingtransceiver is located. Selection of additional transmission cellsadjacent the transmission cell in which the paging transceiver islocated is based on both signal strength and differential propagationdelay measurements. Only transmission cells indicating a received signalstrength of less than 20 dB down from the transmission cell in which thepaging transceiver is located are suitable for selection inpseudo-simulcast operation. Additionally, of the transmission cellssuitable for selection by received signal strength measurement, thosecells then having the lowest differential propagation delays are finallyselected. A final criterion for cell selection is that none of thetransmission cells selected for pseudo-simulcast transmission areadjacent to a different group of transmission cells providingpseudo-simulcast transmission. Adjacent groups of transmission cells maybe selected when actual message transmission is staggered in separatetransmission cycles.

As long message traffic increases, message throughput is increased inthe preferred embodiment of the present invention by maximizingtransmission cell reuse. This means reducing the number of transmissioncells selected for pseudo-simulcast transmission from perhaps originalgroups of four, to three, to two, and finally to the non-simulcast modeof one transmission cell. By utilizing transmission cell reuse andmessage storage, numeric message transmission efficiency can beincreased to fifty percent while long message transmission efficienciesof 96 to 98 percent are possible compared to a fraction of a percent forconventional paging systems.

Implementation of the remote stations, shown in FIG. 6B, is similar tothat of the central station, with the following differences. Linkreceiver 412 receives the burst from the central station. The SACKS,system acknowledgement signals are transmitted from the remote stationsto the central station using link transmitter 428. The output of linkreceiver 412, couples to site controller 430, which operates in a mannersimilar to controller 406 and which further couples to synchronizingmeans 426. The synchronizing means recovers the transmittedsynchronizing signal, adjusting timing means 417 to maintain synchronousoperation of all transmitters within the system with the centralstation.

Coupled to site controller 430 is decoder/error corrector 424 which isused to correct any errors in the active page file information receivedfrom the central station during the burst signal, thereby insuring thetransmission of good data from each remote site station. Error detectionand correction algorithms for signaling schemes, such as for POCSAGencoded addresses and data, are well known in the art. Should it bedetermined the information received from the central station iscorrupted beyond correction at any remote station, the system could beconfigured for that remote station to request a retransmission of theactive page file information, although the operation of such a system isnot disclosed in the present invention. The error corrected informationis stored in memory 404 until the appropriate time to transmit eitherthe address segment or message segment, as previously described.

The paging transceiver of the present invention is shown in theelectrical block diagram of FIG. 7. Operation of the paging transceiveris disclosed in Siwiak et al U.S. patent application No. 07/141,654,filed Jan. 7, 1988, entitled "Frequency Division Multiplexed AcknowledgeBack Paging System", consequently only a brief operational descriptionwill be provided herein. In the receive mode, signals received byantenna 502 are coupled through T/R switch 504 for processing by thereceiver portion of the paging transceiver. The receiver portioncomprises an RF amplifier 508, preselector filter 510, mixer 512, localoscillator 514, buffer amplifier 516, IF amplifier 518 and demodulator520, the operation of which is well known to one of ordinary skill inthe art. Microcomputer 506, couples to the output of demodulator 520 andperforms such functions as address decoding together with memory-EEPROM522 which stores preassigned address information, in a manner well knownto one of ordinary skill in the art. Alert signals generated bymicrocomputer 506, are coupled to audio driver 526 which are thendelivered by transducer 528 also in a manner well known to one ofordinary skill in the art. A display 532 is provided to display thereceived messages which are stored in memory (RAM) 530 after they havebeen received. Microcomputer 506 controls transmitter power output bycontrolling amplifier 550 by sampling the output of threshold detector524 which corresponds to the signal strength of the received unmodulatedcarrier signal as described in patent application No. 07/141,654.Microcomputer 506 together with buffer amplifier 538, divider 540,exclusive-or gate 542, mixer 544, and filter 546 control the transmitterfrequency using the received unmodulated carrier signal as a referenceas described in patent application No. 07/141,654.

Operation of the system of the present invention is shown in detail inthe flow charts of FIGS. 8-10. FIGS. 8 A-C describe the operation of thecentral station. FIGS. 9 A-C describe the operation of the remotestations. FIGS. 10 A-C describe the operation of the paging transceiverswithin the system.

Referring to the block diagram of FIG. 8A, when the system is initiallyturned on, the microcomputer controller is initialized, block 600. Thesystem then waits for a page request generated from a telephone oralphanumeric messaging terminal, block 602. The page request is enteredinto the system, block 604. The information entered is evaluated for thenature of the page to be generated, such as tone only, short message andlong message pages. If the information entered is to be processed as atone only page, block 606, the system assigns functional address 1,block 610, corresponding to the tone only address of a pagingtransceiver capable of receiving multiple page types, such as tone only,numeric or alphanumeric pages. For conventional tone only receiversoperating in the system, functional address 1 corresponds to the normalpaging address. In the preferred embodiment of the present invention,paging transceivers can be assigned up to three functional addressesdescribing the operational characteristics. The purpose for theassignment and use of these functional addresses will become apparent inthe description to follow. Should the information entered be a shortmessage, block 608, such as a message capable of fitting into a singlePOCSAG data block, the system also assigns functional address 1, block610, corresponding to the address of the paging transceiver to which themessage is intended. As in the case of a conventional tone only pagingreceiver, conventional numeric paging receivers are assigned functionaladdress 1 corresponding to their normal paging address. The handling oftone only and short message addresses is shown in FIG. 4. Theseaddresses are included in the current frame address field where they arealways positioned at the end of the address queue in the active pagefile, as shown in block 612, after those addresses assigned to pagingtransceivers having acknowledgment capability, as previously described.

When a long message is to be transmitted, the system assigns functionaladdress 2, block 620, and an ack-back channel, block 622. Functionaladdress 2 is always transmitted at the first data bit rate, such as 1200bits per second, and when decoded by the paging transceiver, indicatesan acknowledgement response is to be generated at the appropriate time.Furthermore, functional address 2 indicates information to follow in thenext transmission cycle will be at the higher, or second data bit ratewhich the paging transceiver is capable of receiving. This informationis stored in the active page file, block 614. The system also assignsfunctional address 3 to the message, block 616, and stores thisadditional information along with an end of message marker in thecurrent frame message file, block 618. Functional address 3 is alwaystransmitted at the second data bit rate and indicates data is to followalso transmitted at that rate. Furthermore, functional address 3indicates the paging transceiver is to switch to the first data bit rateonce the message has been received. This information is held in thecurrent frame message file until the paging transceivers' locations havebeen determined, as will be explained shortly.

The current frame-1 message file is recovered, block 624 and formattedwith the active page file, block 626. Continuing with FIG. 8B, thecontroller continues to monitor when it is time to transmit the burstsignal, block 628, decrementing the frame timer, block 630, andreturning to wait for any additional page requests, block 602. As shownin FIG. 8B, when the controller determines it is time to transmit theburst signal, the information in the active page file is interleaved, ina manner well known to one of ordinary skill in the art, and a blockerror check bit is generated, block 632. Interleaving the data reducesthe transmitted burst error rate when the active page file istransmitted to the remote stations. The controller than switches thetiming to the burst signal rate, block 634, and transmits the activepage file to the remote stations, block 636.

Continuing with FIG. 8C, the central station then switches to remotestation operation, block 638, for the transmission of the active pagefile information within the central station transmission cell. Acomplete description of the remote station operation will be providedwith the description of FIGS. 9 A-C. At the termination of remotestation operation, the paging transmitter is de-keyed, block 640. Thecontroller then selects the SACKS receiver, switching to the burst-inoperation, block 642. The system generated acknowledgement responseswhich include encoded signal strength information is received at thecentral station, block 646 during the SACKS transmission. In thealternate embodiment of the present invention, time of receptioninformation, as well as signal strength information, would have beentransmitted from the remote stations. The encoded signal strengthinformation is decoded, and the information correlated with similarinformation from each responding station to determine the transmissioncell, or cells, in which each of the responding paging transceivers islocated, block 646. Should any paging transceiver fail to respond, aswould happen when the paging transceiver is turned off, has a badbattery, or is out of range of the system, the message corresponding tothat unit is deleted from the current frame message file, block 650, andstored in the active page file being generated for the next transmissioncycle, block 652. It will be appreciated by one of ordinary skill in theart, that it may be more appropriate to delay the transmission of amessage to the paging transceiver which fails to respond, in perhapsfive minute intervals. The current frame message file is recovered,block 654, remote station ID's are assigned to the current frame messagefile for those paging transceivers which responded, and the file is thenstored in the current frame-1 message file, block 656, for transmissionduring the next transmission cycle.

The operation of the remote stations is described in the flow charts ofFIGS. 9 A-C. Referring to FIG. 9A, when the remote stations are firstturned on they are initialized, block 700, which includes selection ofthe link receiver for monitoring transmissions from the central station.Once synchronization signals transmitted in the burst signal from thecentral station are detected, block 702, the remote site clockssynchronize with the central station, block 704. The remote sitestations can then receive the active page file transmitted in the burstsignal, block 706. The active page file information which wasinterleaved at the central station, is deinterleaved at the remote sitestations, block 708. The deinterleaved active page file data can bechecked for errors in transmission, the errors corrected, and themessage segment of the active page file can then be re-interleaved forfinal transmission to the paging transceivers, thereby significantlyreducing the final message error rate. The de-interleaved active pagefile is sorted by the address and message segments. The current frameaddresses to be simulcast transmitted are identified, block 710, andstored in a current address file at each remote site station, block 712.The message segment of the active page file is next sorted for stationID, block 716. Those messages not flagged with an ID corresponding toeach individual station are dumped, block 720. Those messages having anID corresponding to the particular station are stored in a local messagefile, for transmission at the appropriate time, block 718. After thelast message has been processed, block 714, the controller selects thesimulcast transmission bit rate, block 722. The controller then keys thetransmitter, block 724. The sync portion of the address field istransmitted, block 726, followed by the current frame addresses, block728. Continuing with FIG. 9B, after the address segment has beentransmitted, modulation is cut off, and unmodulated carrier istransmitted, block 730. The controller then selects the non-simulcastbit rate, block 732 for those stations having messages to betransmitted. The message transmit timer is loaded, block 734, whichdefines the time for transmission of the message segment, and transmitsthe local message file, block 736. If the message timer has not timedout, block 738, after all messages for a particular transmission cellhave been transmitted, the controller continues to decrement the messagetransmit timer, block 740. When message transmit timer timeout hasoccurred, the paging transmitter is de-keyed, block 741. The acknowledgeresponse time is loaded, block 742, corresponding to the time intervalpaging generated acknowledgment signals are to be received. Thecontroller then selects the PACK receiver, block 744, for reception ofthe PACKS, block 746. Continuing with FIG. 9C, by means of the receivedsignal strength indicator, the controller further determines theacknowledgement response signal strength of all responding pagingtransceivers, block 748. The encoded acknowledgment responses aredecoded and error corrected, block 750, minimizing errors in thelocation of the responding paging transceivers. The encoded signalstrength are temporarily stored, block 752, until it is time to transmitthe SACKs, block 754. If it is not time to transmit the SACKs, theresponse timer is continued to be decremented, block 756, until it istime to transmit. The controller then selects and keys the remote linktransmitter, block 758, for transmission of the encoded signal strengthand acknowledge response information, block 760. After the SACKs havebeen transmitted, the controller again selects the remote link receiver,block 762, in preparation for the reception of the next burst signalfrom the central station.

Operation of the paging transceivers is described by the flowcharts ofFIGS. 10 A-C. Referring to FIG. 10A, each time a paging transceiver isturned on, the microcomputer controlling the operation of the pagingtransceiver is initialized, block 800. The paging transceiver is set tothe simulcast transmission receive rate, block 802. The pagingtransceiver then begins to sample information received on the channel,block 804. If the sync information is not received, block 806, thepaging transceiver continues to monitor the channel, until it isreceived and detected. The address timer is then loaded, block 808, andthe received data is sampled for address, block 810. If datacorresponding to the paging transceiver's preassigned address is notdetected, block 812, the paging transceiver continues to sample datauntil the address timer times out, block 814, or until a preassignedaddress is detected, 816. If the paging transceiver, detects functionaladdress 1 (FA1), block 818, the paging transceiver activates the alertcircuitry, block 820, informing the user a page has been received.Paging transceivers responding to FA1 do not acknowledge in the system,as was previously described. If the address detected is functionaladdress 2 (FA2), block 816, the message flag is set, block 822, and theacknowledge flag is set, block 824. The paging transceiver is then setto the non-simulcast receive rate, block 826. The carrier timer isloaded, block 828, providing the time interval during which theunmodulated carrier is to be detected. Continuing with FIG. 10B, thepaging transceiver locks onto the carrier, block 830, to calibrate thepaging transceiver's acknowledgement response transmitter frequency, andpower level, when required, block 30. After carrier timer timeout, block832, the message timer is loaded, block 834. The message timercorresponds to the time interval the message segment of the transmissionis transmitted. The MF-1 flag is next checked, block 836. If the MF-1flag is not set, block 836, the paging transceiver is in the currenttransmission frame, and any forthcoming messages will not be directed toit. In this instance, the paging transceiver waits for the message timerto time out, block 854, and then loads the acknowledgement responsetimer, block 852. When the MF-1 flag is set, block 836, the currenttransmission cycle is completed, and the next transmission cycle is inprogress. The paging transceiver samples the received information,correlating for address, block 838. Messages transmitted during themessage segment of the transmission cycle are transmitted using thefunctional address 3 (FA3) address, as previously stated. If FA3 is notdetected, block 840, the address detected did not correspond to thatpaging transceiver. Should none of the received addresses match thepaging transceivers preassigned address, and message timeout has notoccurred, block 840, the paging transceiver continues to search for thepreassigned address. If FA3 was detected, block 844, the following data,corresponding to the message, block 844, is received. This data isde-interleaved, block 846, and then stored, block 848. Upon completingthe reception and storage of the message, the user is alerted, block850.

Returning to block 852, after the acknowledgement response timer isloaded, the paging transceiver checks to see if the MF flag was set,block 856 of FIG. 10C. The MF flag indicates the paging transceiver isto provide an acknowledgement response at the appropriate time. Thepaging transceiver then switches to the transmit mode, block 858,transmits the acknowledgement response, either ACK1 or ACK2, block 860.Transmission of an ACK1 response indicates the address received wasreceived without any non-correctable errors. Should the message bereceived with more errors than can be corrected, the FA2 response istransmitted. The acknowledgement response is transmitted until theacknowledgment response timer times out, block 862. The MF-1 flag isthen set corresponding to the MF flag, block 864, and the MF flag isthen reset, block 866, returning the paging transceiver to sample forsync information, block 802 of FIG. 10A.

In summary, a high data rate simulcast communication system has beendescribed which provides efficient transmission of long numeric oralphanumeric data messages. The signaling format of the preferredembodiment of the present invention also may be easily integrated into aconventional POCSAG paging system. Referring back to FIG. 3, it will beappreciated that synchronization codeword 104 together with addresssegment 106 represents a conventional POCSAG batch in both structure andtransmission time. In the preferred embodiment of the present invention,the time interval required to transmit silent carrier 112, messagesegment 114, PACKS 118, and SACKS 120 would be equal in time to a POCSAGbatch. Such a system can support both conventional paging receivers andpaging transceivers as described herein. During those time periods whenno long alphanumeric messages have been entered into the system, thesystem operates much like a conventional POCSAG paging system. As toneonly and numeric messages are received, the paging terminal would formatthem into conventional POCSAG batches distributed about the systemduring the burst signal 102. The sequences of POCSAG batches are thentransmitted in the standard simulcast transmission mode. As longmessages are entered into the system, they would be processed in themanner of the preferred embodiment of the present invention. Aspreviously described, long messages may be accumulated in the localmessage file at the remote site stations until such time as the queue isfull, further enhancing message throughput from any remote site station.As an example, by providing frequency re-use, such as four independenttransmission zones in a typical system for message segment transmission,and increased data bit rate transmission capability, such as 4800 bitsper second versus 1200 bits per second, long message throughput can beincreased sixteen times that of a conventional paging system. Thosefactors limiting frequency re-use, as previously explained, can increaseor decrease the actual long message throughput from the value indicatedin the example above.

While specific embodiments of this invention have been shown anddescribed, further modifications and improvements will occur to thoseskilled in the art. All modifications which retain the basic underlyingprinciples disclosed and claimed herein are within the scope of thepresent invention.

We claim:
 1. A method for transmitting a long text message to a pagingtransceiver in a system comprising a plurality of transmission cellsdefining different geographical areas, each transmission cell having atransmitter for transmitting an address and the message, and a receiverfor receiving an acknowledgement signal generated by the pagingtransceiver, said method comprising the steps of:transmitting theaddress at a first data bit rate, the address identifying the pagingtransceiver, the address being simulcast from transmitters locatedwithin each of a plurality of transmission cells; transmitting anacknowledgement signal from the paging transceiver in response to havingreceived the address; receiving the acknowledgement signal by two ormore receivers located within each of the plurality of transmissioncells; identifying the transmission cells of the receivers receiving theacknowledgement signal for locating the paging transceiver; andselecting the transmitter in the transmission cell in which the pagingtransceiver is located, and at least one additional transmitter in atransmission cell adjacent to the transmission cell in which the pagingtransceiver is located, for simulcast transmitting the address and themessage at a second data bit rate higher than the first data bit rate.2. The method according to claim 1 wherein said plurality oftransmission cells further have a link transmitter and a link receiver,said step of identifying comprising the steps of:deriving informationfrom the acknowledgement signal received in each of the plurality oftransmission cells; transmitting the information derived in eachtransmission cell from the link transmitter to a predetermined linkreceiver; and correlating the information received at the predeterminedlink receiver to identify the transmission cell in which the pagingtransceiver is located and to identify at least one additionaltransmission cell adjacent the transmission cell in which the pagingtransceiver is located.
 3. The method according to claim 1 furthercomprising the steps of:formatting the address and the message withinformation identifying the transmission cell in which the pagingtransceiver is located and the at least one additional transmission celladjacent the transmission cell in which the paging transceiver islocated; transmitting the formatted information to the link receiverslocated in each of the plurality of transmission cells; accepting theformatted information at the transmission cell in which the pagingtransceiver is located and the at least one additional transmission celladjacent the transmission cell in which the paging transceiver islocated; and transmitting the address and the message from thetransmitter in the transmission cell in which the paging transceiver islocated and from the at least one additional transmission cell adjacentthe transmission cell in which the paging transceiver is located.
 4. Asystem for transmitting long text messages, said system comprising:aplurality of transmission cells defining different geographical areas,each having a transmitter for simulcast transmission of an address at afirst data bit rate, and further for transmitting the address and amessage at a second data bit rate higher than the first data bit rate; apaging transceiver, having means for generating and transmitting anacknowledgement signal in response to receiving the transmitted addressat the first data bit rate; a receiver, located within each of saidplurality of transmission cells, for receiving the transmittedacknowledgement signal; identifying means, responsive to the receivedacknowledgement signal in each of said plurality of transmission cells,for identifying the transmission cell in which said paging transceiveris located and at least one additional transmission cell adjacent tosaid transmission cell in which said paging transceiver is located; andselecting means, responsive to said identifying means, for selectingsaid transmitter in the transmission cell in which said pagingtransceiver is located and said transmitter in the additionaltransmission cell adjacent the transmission cell in which said pagingtransceiver is located, for simulcast transmitting the address and themessage at the second data bit rate higher than the first data bit rate.5. The system according to claim 4 wherein said first data bit rate fortransmitting the address is 512 to 1200 bits per second.
 6. The systemaccording to claim 4 wherein said data bit rate for transmitting theaddress and message is 2400 to 4800 bits per second.
 7. The systemaccording to claim 4 wherein said identifying means comprising:a signalstrength indicator, responsive to the received acknowledgment signal ineach of said plurality of transmission cells, for generating signalstrength indication signal; timing means, for generating timing signalsin each of said plurality of transmission cells; and a phase comparator,coupled to said timing means and to said receiver in each of saidtransmission cells, for comparing the timing signal and the receivedacknowledgement signal and for generating a time of reception signal ineach of said transmission cells in response thereto; link transmitters,located within each of said plurality of transmission cells, fortransmitting the signal strength indication signal and the time ofreception signal in each of said plurality of transmission cells; and apredetermined link receiver, for receiving the signal strengthindication signals and the time of reception signals from each of theplurality of transmission cells; and a controller, responsive to thereceived signal strength indication signals and to the time of receptionsignals, for identifying the transmission cell in which said pagingtransceiver is located, and for identifying at least one additionaltransmission cell adjacent to the transmission cell in which said pagingtransceiver is located.
 8. The system according to claim 4, wherein saidselecting means comprising:a predetermined link transmitter fortransmitting the address, the message and information identifying saidtransmission cell in which said paging transceiver is located; linkreceivers, for receiving the address, the message and the informationidentifying the transmission cell in which the paging transceiver islocated; and a controller, coupled to said link receiver, forindividually accepting the information identifying the transmission cellin which said paging transceiver is located and for individuallyselecting said transmitter for transmitting the address and the messageinformation in the transmission cell in which said paging transceiver islocated, and said additional transmitter in the transmission celladjacent the transmission cell in which said paging transceiver islocated.
 9. The system according to claim 7, wherein said selectingmeans further comprising encoding means, coupled to said signal strengthindicator and to said phase comparator, for encoding the signal strengthindication signals and the time of reception signals for transmission.